1. Field of the Invention
The present invention relates to a lamp unit for a vehicle headlamp and more particularly to a projector type lamp unit including a plurality of light source units and a vehicle headlamp including the lamp unit.
2. Background Art
In general, in a projector type lamp unit used for a vehicle headlamp, a projection lens is disposed on an optical axis which extends in a longitudinal direction of a vehicle, and a light source is disposed further rearwards than a rear focal point of the projection lens, so that light from the light source is reflected by a reflector so as to be close to the optical axis.
As described in, for example, Patent Document No. 1 or Patent Document No. 2, there is known a projector type lamp unit like the one described above in which a light emitting device such as a light emitting diode is used as a light source thereof.
In a lamp unit described in Patent Document No. 1, a plurality of light source units each including a light emitting device and a reflector are disposed in a horizontal direction, and by combining together light distribution patterns or light distribution patterns formed by light from the respective light source units, a light distribution pattern of the vehicle headlamp of a light distribution pattern constituting part thereof is made to be formed.
On the other hand, in a lamp unit described in Patent Document No. 2, a plurality of light emitting devices are disposed in the vicinity of a rear focal plane of a projection lens thereof in such a manner as to be arranged adjacent to each other in a horizontal direction, and by combining together light distribution patterns formed as inverted projected images of the respective light emitting devices, a light distribution pattern of the vehicle headlamp of a light distribution pattern constituting part thereof is made to be formed.
Patent Document No. 1: JP-A-2005-317226
Patent Document No. 2: JP-A-2007-179969
In the lamp unit described in Patent Document No. 2 above, because the plurality of light distribution patterns are formed parallel in the horizontal direction, in the event that the respective light emitting devices are controlled to be illuminated or turned off so that, in the plurality of light distribution patterns, only the light distribution pattern which is to be formed in a position where an oncoming vehicle is present is made not to be formed sequentially, the visibility of a road surface ahead of the vehicle can be enhanced without giving glare to the driver of an oncoming vehicle.
However, because these light distribution patterns are formed as inverted projected images of light emitting chips of the respective light emitting devices, the resulting light distribution patterns reflect light emission irregularities inherent in the light emitting chips as they are. Because of this, it becomes difficult to form these respective light distribution patterns with substantially uniform brightness or having specific luminous intensity distributions.
On the other hand, in the lamp unit descried in Patent Document No. 1 above, because the respective light distribution patterns are formed as the inverted projected images of light source images formed on the rear focal plane of the projection lens by light emitted from the light emitting devices that is reflected by the reflectors of the respective light source units, it becomes possible to form these respective light distribution patterns with substantially uniform brightness or having specific luminous intensity distributions.
However, because the light distribution patterns formed by light from the respective light source units have unclear contours, even though the respective light source units are controlled to be illuminated or turned off so that only the light distribution pattern which is to be formed in a position where an oncoming vehicle is present is made not to be formed sequentially, light that forms circumferential edge portions of the light distribution patterns, which are situated on sides of the light distribution pattern that is made not to be formed, enters the eyes of the driver of an oncoming vehicle to dazzle him or her. Consequently, it becomes difficult to control the light source units to be illuminated or turned off in the way described above.